A Kiln Tray filled with Whiting – Video Demonstration

A colleague from Australia – wanting the smoothest possible surface for his kiln-fired painted stained glass – wrote and asked us how we prepared our trays …

We ourselves use whiting (calcium carbonate).

To stop hot glass sticking to the surface of a kiln, whiting is a far simpler solution than, for example, kiln spray, fibre board or kiln paper. And, generally, for a craft which has been going as long as stained glass, the simplest and least technical solutions are best.

Firing your stained glass painting

A kiln-tray filled with whiting

Now the important thing is to make sure the whiting is really compressed.

You must squeeze out all hidden pockets of air, and the surface must be smooth.

Unlike the tray you see in the picture top-right: that tray needs some work …

Now why on earth go to all this trouble?

This is how to stop your glass from sticking when it heats, and how to leave its underneath as smooth as silk.

So turn on your speakers and take a look at this video below: you’ll see what we do. It’s me (David) doing all the hard work, while my inestimable colleague (Stephen) does the voice-over …

As always, your comments and questions are welcome and will be helpful to all the other glass painters who visit here.

Postscript in answer to Bill Wrobel

Our trays are made from mild steel. They are each made from four L-shaped bars which are duly welded together to make a tray with a large hole in the middle. To cover this hole, we insert a neatly fitting piece of fibreboard. The whiting is sprinkled and compressed on top.

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37 thoughts on “A Kiln Tray filled with Whiting – Video Demonstration

  1. Pingback: A Silky Underbelly
  2. Thanks a lot for this, it’s very interesting and informative.

    I have had problems with certain kiln papers reacting badly with painted glass when fired painted side down. Have you noticed any adverse reactions at all with the whiting?

    Also, I am curious as to the provenance of your mild steel trays. Do you have them specially made?

    Seasons greetings to you both!

    • Hi Jackie,

      Thanks for your comment and questions. Like you, we have had problems with kiln paper – probably because it itself is a source of potentially contaminating fumes.

      As for adverse reactions arising from whiting, these have only occurred when, through haste, we neglected to ensure the previously used whiting was as clean as it should have been. Say you’ve painted both sides of the glass and want to fire them in a single firing. Then, necessarily, one of the painted surfaces will be in contact with the whiting. And some paint powder will probably be released into the whiting before the firing. This must be removed before the next firing.

      Similarly, it’s sometimes possible for a single firing to combine tracing and shading on the top surface of the glass with silver stain on the underneath. Once again, some silver stain will probably be released onto the whiting. Once again, this must be removed before the next firing.

      A blacksmith made our trays. But you just need to find a material that won’t warp in the heat of the kiln.

      Every best wish to you, and maybe we will see you again in 2010.
      Stephen

  3. What a splendid idea! So, an inspection of the whiting after a firing is all that is needed? That is, you want to bring it back to the stage it was before firing? Slightly grey fired whiting is OK to use again?

    How thick are the trays and how high is the lip on the trays you use?

    I am going to have a round one made.

    Wonderful video, thank you for sharing it. Your wealth of information and your eagerness to share it is delightful.

    Happy and safe New years to you and yours!
    Shereen

    • Hi Shereen,

      Thanks so much for your enthusiasm and support!

      You ask about re-using dirty whiting. You specifically mention whiting that is slightly grey. And, indeed, this is the colour that whiting will become by virtue of the fumes and dust that is “fired off” in the normal course of firing your painted stained glass. Now this is surface grime. So, typically, it’s fine to continue using this slightly discoloured whiting. But everyone must use their own discretion here. If you’ve spent days painting a piece of clear white glass (as opposed to, for example, deep blue), then it’s no doubt better to use new whiting in order to avoid the slight risk of discolouring your delicate painting.

      Let’s distinguish this “slightly grey” colour (which results from fumes) from remnants of used paint or silver stain. To be clear: it’s essential to remove such remnants of paint or silver stain.

      You also ask about the trays themselves. We use trays made from 1/8 inch gauge mild steel which are ½ inch deep. Ours were made by a local blacksmith. But the main thing is that you need to be confident that the trays don’t warp under the kind of heat to which you will subject them.

      I hope this helps. Please always ask more questions as needed because it’s also useful to other people and allows us to see the other things we need to mention.

      Thanks for your good wishes, Shereen! We too wish you every happiness and success to you in 2010.
      Stephen

  4. I use a large kiln because of the size of the church windows I create. I have been using Plaster of Paris as a cushion on the kiln floor. It seems to work well although it is messy when retrieving fire pieces. The powder will cling to the glass. But it doesn’t stick. – It just has to be brushed off. When laying down a layer of this product I smooth it with a squeegee. Should I press it also?

    • Hello Jack,

      Thanks for your comment. It’s always helpful to us and others to know what works for different people. You ask whether you should also press the Plaster of Paris. Truthfully, now, what can I say? Myself, I’d certainly want to know that all pockets of air had been removed from any powder – whether whiting or Plaster of Paris, or anything else – that I’d used in order to prevent the heated glass from sticking to the kiln.

      Maybe you’re using such a fine layer that there’s no air to expel.

      Can you say?

      Here’s the point: we can tell you and others what works for us – this doesn’t mean it’s the only thing which works. Therefore it’s wonderful that you and others also join in and say what works for you. Thanks so much!

      All the best,
      Stephen

      P.S. Thank you also for sending us an image of the kind of glass painting that you do. It’s always so helful for us to know something of the direction that you are heading for. We’re therefore always glad when you and others send us images of their work. Thank you!

  5. Thank you so much for the video. That technology is perfect for this type of communication.

    Now it looks like there is/are a sheet or two of 6mm fibreboard at the bottom of your tray before you add whiting in the video.

    Is this correct – or is it just more whiting that I am seeing?

    And again thank you for sharing this tip.

    • Hi Bill,

      Thanks for your comment. You are absolutely right in your observation. We should have made this clear in the main body of the post. We will now add a comment there to that effect.

      The tray itself is made from 4 separate pieces of mild steel whose profile is L-shaped. These are then duly welded together to form a tray with a large hole in the middle.

      To plug the hole, we insert a piece of fibreboard which is used pretty much forever because it doesn’t suffer any wear-and-tear.

      Thanks so much, Bill, for pointing out the need for clarification here!

      All the best,
      Stephen

  6. Hello David and Stephen!

    This is rather ‘spooky’! I find I have a few days to spare and thought I would look at achieving a better result when firing using whiting. Just then your email arrived. In a way you have given me some more ‘play’ time now because I shall hurry on over to a super local blacksmith that I know and talk about making a tray (or two?).

    A question: does one have to dry off the whiting in the kiln (just in a pile on the bat) and then sieve it before using it as you describe?

    If this is necessary, then at what temperature and for how long, please? (I have a feeling I may be thinking of plaster of Paris – some years ago before I came and did a course with you two, the guy who taught us said we had to bake out the whiting before using it to work with).

    Clarification would be most gratefully received. And let me tell you how very much I enjoy your frequent messages.

    I wish you a very happy new year!

    All the very best,
    Shelagh

    • Hi Shelagh,

      A very Happy New Year to you as well! And thanks for your comment and question.

      Now we don’t dry out the whiting. We just use it straightaway.

      All the best,
      Stephen

      P.S. As with all these things, different situations can give rise to different results. So the best thing is always to march forward armed with good advice and always be prepared to make your own observations and conclusions.

  7. Stephen and David,

    Thanks ever so much for your continued efforts to promote the excellence of painting on glass.

    I am curious about the gage of the metal you use for the trays shown in the video. Obviously, it isn’t necessary to use 1/4″ steel, but what do you use or recommend?

    Also, did you get the recent referral I sent to you via Allexperts.com. (I noticed some time ago that you all were co-contributors to the site.)

    Again, thanks you all for your generosity.

    Carl Trimble
    Trimble Studios
    Dallas, Texas

    • Hello Carl,

      Thanks for your kind comment. It is indeed our good fortune to have this contact with you. Just imagine that, a mere 10 years ago, we would all of us have been pretty much confined to our studios. And now we can talk like this and discuss ideas together!

      You also asked a question: our own trays are made from 1/8 inch gauge mild steel which are ½ inch deep. As noted earlier, each side of the tray has an L-shaped profile.

      All the best,
      Stephen

      P.S. I can’t be certain we did get your referral from AllExperts. But I’ve checked our inbox, and everything is answered and up-to-date.

      P.P.S. So that other folks know, this is Carl’s profile on AllExperts.

  8. Hello,

    Regarding Bill Wrobel’s question: the fiberboard is 6 or 12mm?

    Regards,

    Mihai

  9. I wondered if I could use this technique when Fusing glass as well as when firing my painting. If I could give up buying kilnwash and thinfire that would make me a very happy woman!
    By the way I spoke with someone who uses play-sand on a kiln shelf if she wants to add a texture to the underside of her pieces. Perhaps that would work with some designs.
    I am off to my local metal smith to place an order this afternoon. THANK YOU.

  10. I want to thank you for all your helpful hints and videos. Living in Oklahoma, I don’t really have any glass painters to learn from but I have watched your videos and read hints for each step of the way and I have to say I am 100% pleased with the quality of the working techniques you have recommend! Leaving nothing to chance, I have practiced and done everything recommended and so far, perfect results. While I am sure I will mess up, so far things are going beautifully. Thank you for giving me the confidence and the tools to express myself in glass painting. There is just nothing like it. You both are a blessing to me.

    • Hello Virginia,

      Thanks so much for your kind comment. It really is also our pleasure. I often hesitate from writing because there is so much self-centred stuff out there, and I always need to be as sure as I can be that the things we write about are really useful (not self-indulgent). So I am glad to know you’re happy. If you are, so are we.

      Always all the best,
      Stephen

  11. Hi there! Great site. Thank you for putting this information out here. I just started doing stained glass again because I now have a workshop in our new house. I bought a small kiln 13x13x9 off craigslist. Do you stack your trays? I learned how to paint glass at the School of the Museum of Fine Arts in Boston but that was a loooong time ago. I think they used to stack the glass on kiln shelves but I can’t remember. My kiln has the elements in the side and it is a front loader. I am wondering whether I can get trays made with short legs on the corners to that I can then stack the trays and fire more pieces.

    Thanks so much,
    Kate

    • Kate,

      We ourselves don’t stack shelves, because our kilns are top-loaders with their elements also in the top. You’ll just need to find out what works for you. And maybe – who knows? It’s your call, your life, your work – you’ll find it works best ‘just’ to fire one shelf at a time (i.e. no stacking) because that gives you the predictable results you want. Do things in your own way – just do them methodically, is all! Because then you’ll know what works, and can change what doesn’t.

      Best,
      Stephen

  12. Hmmm, I’m going to try this. Sick of shelf paper, plus it’s expensive. Any reasons you can think of not to use the dirty whiting I use for lead-light cementing? I can’t think of any problems, particularly since I add lamp black to a batch anyway for a dark grey color. Voila – double duty: no waste at half the price.

  13. I have always used a kiln shelf coated with kiln wash after every firing. This method is used around here (central US) for firing glass stains, slump forming and fusing.

    I was curious if you ever have problems with the metal frames warping from the heat. Is the metal mild steel or stainless?

    I also use kiln furniture to stack trays in the kiln. I was wondering if this would still work or if you recommend having only one shelf in the kiln at a time.

    Thanks,
    Ryan Hill

    • Hello Ryan,

      First up, whatever works for you or anyone else is always fine. I mention this because we haven’t spoken before, and I want to be sure you know how we are undogmatic. Our approach is to explain what works for us and why. You and others then take this as you choose.

      Our frames are made from mild steel. And no, they do not warp: this is because they are not trays as such. Rather, they are constructed from four L-shaped bars, welded at the corners.

      So the frames are hollow in the middle – thus, no flat expanse of metal to warp.

      Next, we cut some fibre board to fit, and plug the hollow. And then – as you see in the film – fill the tray to its lip with whiting, and press it down etc.

      You also ask about kiln furniture and stacking. Again, this is how we work: we have kilns which don’t have shelves. This is because we prefer to make as sure as possible that all glass gets equal heat.

      I wouldn’t have a general recommendation about one shelf or several in the kiln. But, specifically, there are many times when I know that one is more predictable: like when you’re firing stain.

      All the best,
      Stephen

  14. Does anyone know if I have to buy calcium carbonate specifically manufactured for glass work or will any calcium carbonate ground limestone do? It is just so much cheaper to buy elsewhere!

    • We certainly bought ours from a builders’ merchant (not from a glass stockist). As with everything, you’ll just need to run some tests, because nothing but proof is ever good enough.

      • Stephen,

        Just gave the tray idea a go and quickly realized that, although I was using a piece of float glass, the scraping of the glass against the edges of the tray must have started to chip the edge of the glass, and obviously my surface was not coming out smooth. To say nothing of the chips that I ended up fishing out of the tray. What kind of glass are you using? Do you have this problem? I was thinking that I could maybe use a long bevel. but then it is probably too thin to do the job.

        Ekaterina

        • Ekaterina,

          You make a good point which will also help others. We don’t use e.g. toughened glass or anything like that to do this job. Just ordinary float glass. Admittedly it’s fairly thick, but that’s perhaps its main distinguishing feature.

          This makes me wonder about the impact of three variables: (1) how much pressure we / you exert, (2) the angle of our glass, and (3) whether our trays in fact have a smoother finish than yours.

          So leave this one with me while I consider things further.

          Best,
          Stephen

          • Just to help out a bit … My tray is an actual commercially manufactured serving tray with very smooth rounded lip. I put barely any pressure on. I do about 30-40 degree angle when dragging the glass.

            Ekaterina

            • Thanks: very useful. This may now turn out to be one of those situations where we ourselves don’t do things in the best way. We don’t get shards. So something we do is different. Maybe the glass is harder. Maybe it’s gone ‘beyond’ splintering. Whatever: the fact is, if you get different results, then we need to be more specific. Unfortunately, we use an old piece of glass whose origin we can’t be certain of. (Maybe it was blessed by Gandalf.)

              So, for now, one thing I’d suggest is, try using a smaller piece of glass: one that fits just inside the edges of your tray. Sure, this will leave a ridge of whiting around the edges, but this doesn’t matter. Another option is to compress the whiting with not glass but something different. Maybe metal. Maybe polycarbonate.

              The next time we’re in town – it doesn’t happen often – we’re going to get a plasterer’s skimmer and see how that works.

              Thanks for your question.

              Best,
              Stephen

              P.S. As was mentioned in one of the earlier conversations, our trays are made from T-sections which our blacksmith welded together. This means there’s a hollow in the middle which we fill with thick fibre board. The hollow in the middle helps prevent buckling, because the surface area is small. I mention this in case it’s something you need to watch for with your tray, which, I understand, is not hollow like ours is. Maybe it’ll work fine. But just be aware it may buckle in the heat.

  15. I was looking at your firing table and was wondering what the 9999 deg. on the chart with water-based paint in Phase 2 &4 And then again on the chart involving flooding or oil in Phase 3 & 5. Doses this mean that that rate could vary or what?

  16. Hello David and Stephen,

    Thanks you for this very useful video. Hopefully, I shall have one of these trays made up soon.

    Could you confirm for me please the hight of the fibreboard you have used here?

    All the best,
    Sue

  17. I am intrigued by your method. I use thin fire and kiln wash on shelves. I am interested in doing some experimental work. I wish to ask you if you have ever done a pot melt over one of these prepared as you do? It made me think of using your method; then using a screed board with about 1/2″ depth, measure the glass – to just fill this form, so there’d be 5 sides with chalk. Would dripping glass cause the pressed chalk to split or not hold up? (I know I can experiment, but if you know it won’t work, I’ll forego the waste of time.) I look forward to your reply. Thank you for your site and the good information. KaCe

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